The present invention is directed to a system and method for controlling fluid flow within a tube of a heat exchanger. More particularly, the present invention relates to a system and method for controlling flow rate of fluid in a heat exchanger where the flow direction of fluid therethrough is switched or reversed, in order to cause a brush mounted within the tube to move therealong, thus cleaning the interior of the same.
In a heat exchanger of the shell-and-tube type which has been widely known in the art, cleaning of a tube therein is carried out by operating a directional control valve for switching or reversing flow direction of fluid supplied to the heat exchanger tubes. This causes a brush that is received in certain brush capturing devices or chambers disposed at opposite ends of the tube, to move therealong, thus automatically cleaning the interior of the tube.
However, such a conventional cleaning system is disadvantageous in that flow rate or velocity of fluid within the tube is decreased depending upon operating conditions, to such a degree that the brush fails to move along the tube when the flow direction of fluid therein is reversed by the directional control valve. Thus, cleaning of the interior of the tube is rendered virtually impossible. Such decrease of flow rate within the tube also causes the brush to block the interior of the tube when it stagnates therein. This results in problems such as failure of heat transfer, e.g. overheating, along with deterioration of the fluid flowing therewithin.
Additionally, a conventional refrigerator having an automatic tube cleaning device incorporated therein, in which a heat exchanger as described above is utilized, is adapted to detect the load of the refrigerator (e.g. the load of fluid to be cooled within the evaporator such as cool water, the temperature of this cool water during the operation of manufacturing the same, or the load of fluid to be heated, e.g. hot water from a condenser in a heat pump during the operation of manufacturing hot water) without controlling the flow rate of the heating or cooling medium (e.g. the cooling or heating water), or without controlling the flow rate of the cool water itself, and then control the capacity of the refrigerator based upon a signal from the load thereof.
In such a conventional refrigerator, the cleaning of a tube of a condenser and/or an evaporator therein is carried out by switching the flowing direction of the cooling water (or hot water) and/or the flow direction of cool water to the condenser and/or evaporator, by means of a direction control valve, to reverse the fluid flow in the tube, thereby carrying out automatic movement of a cleaning brush received therewithin. Such automatic cleaning of the tube is smoothly accomplished because the flow velocity of cooling water (or hot water) or fluid to be cooled such as cool water, is above the minimum flow velocity of fluid necessary to carry out automatic movement of the brush (hereinafter referred to as "limit flow velocity" or "limit flow velocity for automatic movement of the brush").
However, a recent refrigerator has been developed for the purpose of energy conservation, which has been constructed to effect the control of cooling water (or hot water) or cool water, as well as control of capacity of the refrigerator based upon the detected load of the refrigerator itself (e.g. the load of cool water such as the temperature of cool water during operation of the manufacture thereof, or the load of hot water such as the temperature of hot water from a condenser in a heat pump during the operation of preparing the hot water). More particularly, such a refrigerator is adapted to decrease the flow rate of the cooling water (or hot water) or cool water when the load is reduced. However, the refrigerator of such type which is adapted to control the flow rate of cooling water (or hot water) or cool water, entails the following problems or difficulties when automatic cleaning of a tube by automatic movement of a brush therein, is to be carried out. One such difficulty is that the brush in the tube fails to automatically move when the flow velocity of cooling water (or hot water) or cool water within the tube is decreased below the limit flow velocity for the automatic movement of the brush, thereby rendering cleaning of the tube virtually impossible.
Another difficulty is that stagnation of the brush within the tube due to clogging causes deterioration of heat transfer, resulting in a surging phenomenon in a centrifugal refrigerator, or in a high pressured trip due to condensation. Such a problem is also caused depending upon operating conditions during switching of the flow direction within the tube, because the flow rate of cooling water in the tube instantaneously reaches zero during the flow directional change. For example, this problem occurs under conditions where the capacity of the refrigerator and the internal pressure of the condenser are increased, during the switching of the flow direction.
A further problem is that there is a danger that cool water could become frozen due to a temperature drop within the cool water when the brush is clogged therewithin, thus causing the cool water to stagnate within the tube.
A still further problem is that because the flow rate of cool water instantaneously reaches zero as noted above, there is a danger that cool water could become frozen depending upon operating conditions during the flow directional switching and depending upon the temperature of the cooling medium itself within the evaporator, that cools the fluid to be cooled, such as the cool water.